Place both flours, baking powder, sugar, cocoa powder and ½ cup chocolate chips in a food processor. Pulse until chocolate chips are finely ground. While the processor is running, add canola oil in a low stream. Scrape sides and pulse until combined. Place chocolate mixture in a large bowl.

Add chopped zucchini to food processor and pulse until finely chopped (you should have about 1½ cups). Add zucchini to chocolate mixture.

Place eggs and yogurt in processor and pulse until blended. Add to zucchini/chocolate mixture. Mix until just combined. Fold in remaining chocolate chips.

Divide batter among muffin cups until almost full. Top muffins evenly with 1½ tablespoon of sugar. Bake in middle rack of oven for 20-24 minutes.

Cool on wire rack for 5 minutes. Keep in airtight container at room temperature for 3 days (If it's hot the sugar tops may melt a bit).